The semiconductor device industry has a market driven need to reduce device failures at electrical test. Reduced device failures may result in increased IC fabrication yield and improved device operational lifetime. Increased IC fabrication yields may result in decreased IC prices, and improved market share.
It is well known to examine failed devices by means of electrical testing, optical microscopes, transmitting electron microscopes (TEM), scanning electron microscopes (SEM), and other methods. If, for example, a contamination particle is found that produces a short between two conductive lines in a signal layer, then action may be taken at the fabrication site to reduce particle levels, and thus increase fabrication yield. If a metal contact has been under etched and has thus produced an open circuit state, then action may be taken at the fabrication site to improve surface tension in wet chemical etches, or to increase the overetch time to help ensure that the contacts are properly opened.
It is known to remove the top layers of an IC device by means of what may be known as a spot etch, in which a small elastomeric ring formed of a chemically resistant material is pressed onto the surface of the IC in the area of the suspected defect and serves to hold an etching solution designed to remove some or all of the top layers of the structure and expose the defect. However, the size of the elastomeric ring is very large as compared to the dimensions of typical structures, such as ICs, and may be larger than 2 mm in diameter, and thus produces a relatively large hole in the IC device. In addition to the above noted issue of the size of the opened area of the circuit, there is no method to image the surface during the material removal process to determine if the etch position coincides with the suspected defect, or to determine when the etch has reached the desired location.
It is known to etch small diameter holes of several microns in diameter in IC surfaces by means of what may be known as ion milling, using focused ion beams of such heavy materials as gallium. It is possible to analyze the material being etched by means of examination of the atoms in the exhaust gas stream, typically using methods such as optical emission spectroscopy, atomic absorption spectroscopy, infrared spectroscopy, Raman spectroscopy, or mass spectroscopy. However, ion milling is not generally able to selectively etch certain types of materials, such as oxide over metal, with a reasonable etch ratio, as compared to the high selectivity available with the chemical spot etching discussed above, and it is difficult to determine when the vertical etch depth has reached the desired location.
In addition to the above noted problems with exposing a suspected defect location, there is no method to correct the defect so that the device can be retested to determine if the suspected defect was the sole problem with the IC. In addition to the ability to prove that the suspected defect was the cause of the failure, such an ability to repair an IC would also be useful in saving the lost value of high value ICs, such as fast microprocessors and radiation hardened logic chips.
What is needed is a method to chemically etch a small area of an IC with high selectivity between different materials, with the ability to then either etch away unwanted material, or to deposit a material to replace a missing section, and then repair the etched hole in the IC. The ability to observe the etching process and to end etching at the desired defect location as well as to analyze the etch reaction products may help to provide an accurate etch stop procedure. With such an arrangement, the IC may have the defect location easily found and exposed, the defect cured, and the part returned to operational condition.